This invention relates to longitudinally movable bearing structures having raceways for guiding or continuously circulating rolling elements, such as balls. The invention is particularly directed to the provision of raceways for such bearing structures, for avoiding problems arising by the passage of the rolling elements to the loaded portions of the raceways. While the invention is particularly disclosed with reference to ball bushings adapted for longitudinal movement relative to a shaft, it will be apparent that the invention can be adapted for other uses.
In ball bushings of one type, adapted for longitudinal movement relative to a cylindrical shaft, the bushing is comprised of a housing or casing structure surrounding the shaft and defining raceways for the balls. The raceways have longitudinally extending portions with radially inwardly open slots, for balls under load engaging the shaft, and longitudinally extending raceways separated from the shaft for balls not under load, and generally semicircular end sections interconnecting the ends of the two longitudinally extending portions.
Bushing structures of this type are well known. In one form of bushing of this type, the ends of the raceway portions for the balls under load are provided with conical shapes, intended to guide the balls from the unloaded raceway portions into the loaded raceway portions without restraints. This structure has been found to have the disadvantage, however, that unloaded balls, upon entering the loaded section of the raceway, strike against the edges of the raceways at the same time that they are placed under load. This results from the fact that unavoidable tolerances, for example, due to manufacturing, result in small displacements of the raceways in the loaded and unloaded portions thereof. As a result, a damaging stick-slip movement of the balls occurs, with consequent blocking of the balls and the production of undesirable running noise of the balls in the raceways. Further, since the ends of the raceways are conical, the balls in this region are not under load, whereby the stiffness of the machine structure is decreased, as well as the load capacity of the bushing.
The present invention is thereby directed to the provision of a bearing structure of the above type in which the rolling elements may run in their respective raceways without a damaging stick-slip movement, and wherein the load capacities of the bearing structures may be increased, with consequent noise reduction.